1. Field of the Invention
This invention relates to a method for recycling metals from swarf, particularly to one capable to separate oil in swarf by means of aqueous surfactant solution within thirty minutes with oil removing efficiency as high as more than 99%.
2. Description of the Prior Art
Grinding and cutting operation is a cutting process that removes material from the workpiece by the action of abrasive grains. It is the most important process in the metal working industry that manufacture high speed cutting tools, bearings, and special metal devices. In order to increase smoothness and lower temperature in grinding and cutting and enhance the surface quality of the workpiece cutting fluids is commonly used, resulting in swarf of metal mixed with cutting fluids.
As the metalworking industry has been growing year and year, swarf produced has been increased substantially, and some sward may contain chlorinated compounds and heavy metals belonging to harmful toxic waste, and its treatment has been looming up as a serious problem.
For example, metalworking industry in South Carolina State in USA, swarf produced every year surpasses 3 million tons, and that produced in the whole world may be extremely enormous, directly threatening business of the metalworking industry. Swarf particles are 1–10μ in their diameter, having economic worth. After swarf is compressed and filtered dry, there are still 30–50% oil remaining in it, and it is very risky to directly dissolve owing to potential explosion, If it can be separated, recycled, its treatment problem can be solved, saving dispenses for treatment and recovering recyclable oil and metals, having function of waste treatment and resource recycle as well.
In Taiwan ten thousand tons of swarf is produced every year, and liable to increase year by year, with the expense for treating also increasing day-by-day, seriously affecting existence of the metalworking industry. As swarf contains 30–50% cutting oil, the oil is apt to catch fire during its transporting, and its treatment depends almost on dissolution or burial in the ground. If it is dissolved, metals can be recovered for recycle, but oil is impossible to be recovered and residue has to be disposed of. But any useful resource is impossible to be recovered in case of burying.
For the present, no commercialized washing art for swarf are available, and a method for recycling sward under study is performed by washing with aqueous surfactant and extraction with supercritical carbon dioxide (SCCO2). Extraction with the Supercritical carbon dioxide needs the condition of an atmosphere larger than 78.0 and of the temperature of 31.1 degrees, and the pressure commonly used in handling is generally larger than 100 atmosphere, in addition to expensive equipment, so it is not so prevalent, The relative research disclosed that aqueous surfactant solution on the market is substantially effective in removing nonaqueous organic pollutants and oils from substances containing soil and sand, CFC-113 used recently as washing solution is limited in its effectiveness, so another washing method is now under research and development for some industry.
The step using the surfactant solution for washing swarf is very similar to the soil washing, involving mixing dry swarf (not yet treated swarf) with the surfactant solution, and producing two flow processes. One is for clean and wet swarf and the other for emulsifying oil solution. The former process is to separate metal powder from clean and wet swarf by means of a magnetic device. The latter process is to send the already separated metal powder to a steel factory for recycling and reuse. The large quantity of aqueous emulsion has to be treated and removed of the pollutant (the surfactant and the cutting oil) contained in it. In this washing art, it plays a critical role in the economy to recycle and reuse the surfactant, which is quite expensive.
Nowadays many commercial surfactants used in research in foreign countries are as follows.
SA-8 of Amway corporation, Dowfax of Dow Chemical Company, CDE/A6, CDE/A6, BQ6, AMT of Albright Wilson, AquaTek of Rhone-Poulenc, and Micro of International Products. Their oil removing efficiency is shown below, being between 86–98%, needing many times and 1–6 hours for washing. As there are disadvantages that a large quantity of washing solution is required, the time needed for washing is long, and the solution after washing cannot be reused, those surfactants have to be improved. In addition, they are rather priced high, so a cheaper surfactant is to be found to take place of them.
South CarolinaSouth CarolinaUniversity,UniversityResearchChemical Eng.Mineral ProductInstituteDept.Research Dept.Wash time45375Wash efficiency86.098.1